1. Field of the Invention
The present invention relates to a cell culture plate suitable for use in bioassay to evaluate the effects of drugs or to test the toxicity of drugs with the use of cultured cells and a method of manufacturing the cell culture plate.
2. Description of Related Art
A technique of using cells isolated from tissue for tests and inspections is essential in biotechnological fields. This technique is widely applied to diagnosis on disease and pathology, search for new drugs and determination of drug efficacy, animal inspection, plant inspection, environmental pollutant test and so on. Though isolated cells are sometimes used immediately for test, in many cases they are cultured in a culture dish or a test tube by a cell culture method. Various inspections are conducted in a culture system.
The assay normally sets uniform culture systems and checks the efficacy of drugs to be evaluated with varied amount and concentration. It thus uses cell culture vessels that are formed uniformly. The culture vessel is typically a culture dish. 6-well, 12-well, 48-well and 96-well plates are generally used as culture dishes. Further, due to the recent trend of use of minute amounts, a 384-well plate having a number of culture dishes with small bores has been used lately.
However, use of a commercially available cell culture dish for culturing tissue cells causes the cells to be thinned into a form in lack of direction and to cease to express the features observed in vivo. This is because the culturing on a well plate, which is vessel shaped, is substantially the same as the culturing on a flat plate for a cell with the size of several μm to several tens of μm. Particularly, in the growth of tissue cells that are difficult to culture, such as hepatic cells, it is further difficult to maintain the features they have in vivo.
An approach to overcome the above drawback is to form a minute uneven pattern suitable for the growth of tissue cells on a culture plate and culture the cells on the plate. This approach aims at arranging the cells on the minute uneven pattern and growing them sterically with direction. This technique, however, fails to bring out the features observed in vivo by the growth of the cells due to lack of keeping the freshness of culture solution.
A normal cell culture process soaks a culture plate in culture solution for one to several days. As a human body receives oxygen and nutrients through blood in vivo and expels waste products, a cell receives oxygen and nutrients from culture solution and expels waste products into the culture solution. The waste products affect the growth of the cell, and thus the culture solution is replaced a plurality of times when conducting the cell growth for several days, which causes the solution freshness to vary, thus failing to maintain the features observed in vivo.
In order to preserve the same culture environment while varying the culture conditions in one culture plate, a technique of changing culture areas is proposed, for example, in Japanese Unexamined Patent Publication No. 11-169166. The technique uses a culture vessel in which culture dishes whose cell culture areas vary at given rate are arranged in succession. The culture dishes, for example, have the culture areas that vary successively like 100%, 75%, 50%, 25% and 0%. It is thereby possible to control the number of culture cells without changing the culture environment, which enables the use of the culture plate for bioassay in various conditions.
As described above, the use of a conventional cell culture dish causes cells to be thinned to cease to present the features they have in vivo. On the other hand, culturing cells on a minute uneven pattern in order to grow the cells sterically with direction decreases the freshness of culture solution due to waste products discharged into the culture solution, and the cells thereby do not present the features they have in vivo.